In a semiconductor device, an element isolation region is formed to demarcate an element-forming region. The element isolation region is formed by means of an STI (Shallow Trench Isolation) formed by filling a groove in a semiconductor layer with an insulating film. With regard to STIs, recent miniaturization has made it difficult for the STI groove to be filled with an insulating film using a CVD method or the like, and as measures to overcome this problem, methods have been proposed in which the groove is filled with a silicon dioxide film formed using an SOD (Spin On Dielectrics) method or a flowable-CVD method, with which a film can be formed by applying polysilazane or the like.
As described for example in patent literature article 1, the structure of the STI comprises a liner nitride film and an SOD film and/or an oxide film (HDP film) formed using a high-density plasma-CVD method (High Density Plasma-CVD: HDP-CVD). Further, patent literature article 1 describes the use of a structure having a liner nitride film and an SOD film for STIs having a small isolation width in a memory cell region, and the use of a structure having a liner nitride film, an SOD film and an HDP film for STIs having a large isolation width, provided in a region at the boundary between the memory cell region and a peripheral region.
Further, patent literature article 2 describes, as an STI, a structure having a wall oxide film and an element isolation oxide film, the element isolation oxide film comprising an SOD film and/or an HDP film. The literature also indicates that a liner nitride film and a liner oxide film are further provided between the wall oxide film and the element isolation oxide film. Further, patent literature article 3 describes a structure with which, when a flowable silazane compound is deposited using a flowable-CVD method into grooves having different isolation widths, in which a liner oxide film and a liner nitride film have been formed, grooves having a small isolation width are filled, while grooves having a large isolation width are not filled, and this literature article discloses a method in which grooves having a large isolation width are filled by forming an HDP-CVD oxide film after the silazane compound has been converted into an oxide film and has been densified.